It is increasingly common in the oil and gas industry to use hydraulic fracturing (colloquially known as “fraccing” or “fracking”) to aid in the recovery of hydrocarbon fluids such as crude oil and natural gas from subsurface formations. Hydraulic fracturing is a process involving the injection of a “fraccing fluid” (or “frac fluid”) under pressure into spaces such as cracks and fissures within a subsurface petroleum-bearing formation, such that the fluid pressure forces the cracks and fissures to become larger, and/or induces new fractures in the formation materials, resulting in more and/or larger flow paths through which hydrocarbon fluids can flow out of the formation and into a well drilled into the formation. Fraccing fluids typically carry particulate materials called “proppants” that are intended to stay inside the enlarged or newly-created subterranean fissures after the fraccing fluid has been drained out of the formation and hydraulic pressure has been relieved.
There are various different types and formulations of fraccing fluids, but regardless of the type of fraccing fluid being used, one thing common to all fraccing operations is the need for temporary storage of very large volumes of fraccing fluid at the well site, both to provide a reservoir of frac fluid for injection into subsurface formations, and to store frac fluid circulated out of the well after completion of fraccing operations. Storage tanks having volumes of 250,000 to 2,500,000 U.S. gallons or more are commonly required for this purpose.
For practical and environmental reasons, such tanks are typically of modular design so that their components can be shipped by truck to remote well sites, where they can be erected on site and eventually disassembled and shipped off site after they are no longer needed. Open-top liquid storage tanks most commonly are circular, as this is the most stable and efficient structural configuration for a liquid storage tank. Modular circular tanks typically comprise multiple horizontally-curved steel wall panels having a radius corresponding to the radius of the finished tank. The vertical side edges of each curved wall panel abut and are fastened to the vertical side edges of adjacent wall panels by suitable structural connection means, such that when all of the wall panels have been erected and interconnected, they form a circular tank having a particular height, diameter, and liquid storage capacity. A suitable liquid-tight liner is then installed inside the tank, covering a prepared ground surface inside the tank perimeter and extending up and typically over the tank wall. The tank is then ready to receive a fraccing fluid or other liquid that needs to be stored.
Environmental regulations require storage tanks for many different types of liquids to be provided with secondary containment means to protect against environmental contamination in the event of a tank leak. For example, petroleum storage tanks are commonly constructed within a containment reservoir formed by earthen berms lined with synthetic liners or engineered clay liners installed or constructed below the ground surface. Such secondary containment means may be practical for “tank farm” installations where the primary liquid storage tanks are essentially permanent. However, they are not a practical or acceptable option on well sites requiring tanks for temporary storage of large volumes of liquid (such as fraccing fluid) and where such temporary tanks must be demountable so as to cause little or no permanent environmental disturbance in the area where the temporary tanks were constructed.
One known way of providing secondary containment is to build a primary storage tank within a secondary tank structure, such that if the primary tank should develop a leak, the secondary tank will provide a second line of defence against liquid leakage into the surrounding environment. The present disclosure teaches an innovative process for constructing a primary open-top storage tank within a secondary containment tank without significant disturbance to the environment.